4 Things to Know About Sizing a Pool Heater for 15,000 Gallons

A 150,000 BTU gas heater is the right size for most climates. This follows the general rule of 10 BTUs per gallon, which heats the pool a couple of degrees per hour in moderate weather.

Bump to 200,000 BTUs if you live in a cold climate or want to swim in spring and fall. Nights below 60°F even in summer or extended shoulder seasons justify the extra capacity.

Anything over 250,000 BTUs wastes gas and shortens the heater’s life. It flash-heats the water, causes short-cycling, and costs more than necessary.

Heat pumps work differently and should be sized by surface area, not BTUs. They are slower but cheaper to run, so use a different sizing method for them.